"Not sure where you got this photo. I posted it to friends only on FB. You reposting it to Twitter is way uncool," Zuckerberg tweeted to @cshweitz, according to a screenshot of the tweet grabbed by BuzzFeed.

The Twitter user, Callie Schweitzer, apologized, explaining that she follows Randi Zuckerberg on Facebook and saw the picture at the top of her News Feed.

Randi Zuckerberg said she accepted the apology a few minutes later and explained that Schweitzer probably saw the picture because Schweitzer is Facebook friends with Randi Zuckerberg's sister, who was tagged in the photo.

Photos that have been tagged are visible to friends of every user in the photo, not just the friends of the user who posted it. It is one of the loopholes in the social network's privacy feature that some users say should be plugged.

Many of the tweets by both users, including the one with the photo, have since been deleted.